The present invention relates to an energy-saving method for the wireless reception of data modulated on a carrier signal.
A known, integrated receiver circuit for such an infrared remote control receiver, which has a digital gain control, is the T2521B circuit from the company ATMEL Germany GmbH. The principle of operation of such a circuit is that the carrier modulated signal—the received signal—received from a photodetector, as a rule a photodiode, is fed into an input circuit. The input circuit has a transimpedance amplifier which amplifies the pulsed input current signals and converts them into voltage signals. These voltage signals are then processed in a signal conditioning means. The signal conditioning means has a control amplifier, a limiter and a bandpass filter. In this connection, the task of the control amplifier is to amplify the output voltage from the transimpedance amplifier in accordance with the control specification. The task of the limiter is to limit the signal level swing in order to avoid overmodulation of the bandpass filter. The bandpass filter enables selectivity of the receiver and limits its bandwidth The signals at the output of the bandpass filter are evaluated in a demodulator as an evaluation circuit. This demodulator consists of comparators, an integrator and Schmitt-trigger and generates a switching signal for a driver transistor functioning as a switch, as a result of which a digital control signal is made available to a microcontroller, for example, for further processing.
This known circuit also contains a digital gain control, through which the gain of the receiver is tuned according to an interference field, by means of which high sensitivity for the received signals is attained, however at the same time interference factors, which could arise from an external light for example, are substantially suppressed.
Such a known circuit for infrared remote control receivers has, as a rule, a current consumption from 1 mA to several mA. This means that, with battery driven receivers, an adequate battery service life of around one year is not given in the case of permanent readiness to receive.
An attempt is therefore made to realize energy-saving operation with lower average current consumption by means of externally cycling the supply voltage, and thus increasing the service life of the batteries to more than one year. Such a method for operating an infrared receiver is known from EP 0 663 733 A1, in which this infrared receiver is connected via an interval switch to a battery-fed circuit for the supply voltage, and Via this cyclically supplied with electrical energy. The intermittent operation is suspended, in that the receiver circuit is linked to the supply voltage, by a start signal, the duration of which exceeds the duration of the switching intervals of the interval switch. As a result, the receiver becomes ready to receive by means of a power-on reset (POR) and remains uninterruptedly linked to the supply voltage for at least the sending time of the control signal transmission following the start signal. In so doing, the amplifier stage of the receiver is set to about half of the maximum sensitivity. As the control for remote control receivers preferably works in the 100 millisecond range, the sensitivity to optical useful signals may be less by a factor of 2 directly after start up. If the interference environment here is, on the one hand, too great, so that the amplifier setting is too high for this environment after the POR, the correct reception of useful signals is only possible with an increased bit error rate. On the other hand, the maximum sensitivity cannot be attained in an interference-free environment. Moreover, the maximum response time to a remote control command should not exceed 200 ms. This period of time corresponds to the interval period during which this receiver is in operation. A maximum “on time” of 1 ms must be maintained in order to reduce the average current consumption to, for example, 5 μA. This known receiver operated in this manner may well have a sufficiently low current consumption, however the settings which determine the properties of the receiver or the gain properties are lost because of the cyclical disconnection of the source of energy, as a result of which the receiver has to work with the starting state again, which may have either a less sensitive, i.e. a reduced range, or a too sensitive setting, i.e. an increased bit error rate. The area of application of such a receiver is thus severely limited.